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The present invention relates to a harmonic drive according to the preamble of the main claim.
The functionality of such a harmonic drivexe2x80x94also known as a wave drive or ring band drivexe2x80x94as a very strongly reducing, self-limiting system having a driven shaft coaxial to the drive shaft, is based on a rotating wave generator revolvingly radially deforming an internal geared wheel hoop, also referred to as a flexible band, and therefore its external peripheral surface revolvingly pressing locally outward against the hollow cylindrical internal peripheral surface of slightly greater circumference of a stationary internal gear used as a dimensionally stable support ring which is fixed to the housing. As a consequence, the internal geared wheel itself or its wheel hoop, mounted thereon as a rotatable wheel rim, rolls in the support ring frictionally via friction surfaces or positively via teeth, the wheel and/or its hoop rotating slower than the drive core of the wave generator, which is driven by a motor, according to the difference in circumferences. This rotational movement, which is greatly slowed in relation to the actuation, is preferably transmitted via the external teeth of the wheel rim to the internal teeth of a further external ring, the driven ring, which is concentric to the support ring but not stationary, rather, in contrast, coaxially rotatable, and which is designed in a cup or cap shape, for example, and which is equipped with a driven shaft mounted in the drive housing. A further reduction of the rotational velocity may occur in the teeth from the internal geared wheel to the driven ring due to differing circumferences (number of teeth). The wave generator is typically driven via a low voltage DC motor, coaxially flanged on, which is high-speed and therefore available very cheaply, whose rapid rotation is thus reduced into a much greater torque corresponding to a much slower rotational movement, which has many applications, such as an actuator for motor and climate management and for other functions in a motor vehicle, particularly those replacing manual interventions.
(1) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98.
In the embodiments of such a harmonic drive known from German Utility Model 2 96 14 738, which thus forms the species, and described in more detail in the article xe2x80x9cGenial einfachxe2x80x9d by H. Hirn (KEM Antriebstechnik issue 10/1996), a non-round (for example triangular or preferably oval in axial cross-section) drive core is rotated concentrically in the hub of a radially deformable internal geared wheel as a wave generator. This internal geared wheel may be a one-piece injection molded part having spoke-like, radially oriented tappets between the radially deformable internal geared wheel hub and the externally toothed internal geared wheel hoop, which is also radially deformable. Spokes, which are dimensionally stable lengthwise, between the hub, which is radially deformed by the drive core, and the hoop have the effect that the external teeth of the hoop, corresponding to its revolving radial deformation, only engage over a limited curved segment, which moves around the circumference, with the inner teeth of the support ring.
The present invention is based on the technical problem of indicating a compact construction for such a harmonic drive, already proven in practical use, which is nonetheless easy to mount and usable in many ways.
According to the combination of features of the main claim, the object is essentially achieved in that, for a harmonic drive which is not problematic to manufacture precisely, the internal teeth of the support ring are no longer an integral component of the drive housing, but rather are mounted on a housing baseplate after separate manufacturing and then overlapped by a housing cup, to be attached separately next to it. In this way, exact concentric running of the toothed components to one another may be ensured. The cup receives the central drive shaft of the cap-shaped drive ring in a cantilever mounting, while the baseplate does not fulfill any direct bearing functions for rotating drive parts. On the other hand, reaction forces of the drive are only absorbed by this baseplate; it may therefore not impair the bearing function of the other housing part, which additionally has a radially centering and axially guiding effect due to its fixing on the baseplate. The outside of the baseplate may have different geometric layouts for mounting on different available drive motors.
The internal geared wheel is therefore centered not directly via the baseplate, but rather using the drive shaft which projects through the baseplate. Their indirect engagement in the sleeve-shaped drive core also provides the advantage of dispensing with mounting in the drive housing at the driving end, because this bearing function is assumed outside the drive at the driving end. This allows direct mounting in front of the drive without interposing a coupling element and therefore produces an axially short construction of a very strongly reducing drive motor.